The fanfic could feature characters training their Pokemon with the ocean as a backdrop, or it might involve a special event on the beach where Pokemon show off unique skills. Maybe there's even a quest to save a stranded Pokemon or solve a mystery related to the beach's history.
Well, you might expect Pokemon having fun in the sun, maybe discovering hidden treasures in the sand or encountering mysterious Pokemon that only show up near the shore. There could also be friendships formed or challenges to overcome related to the beach environment.